Method for startup of production in an oil well

ABSTRACT

A method of startup of oil production in a gas-lift well in which inlet flow (22) of gas is controlled (46, 42) while means (34, 28) controlling fluid flow from the well is progressively opened. Preferably, fluid flow rate from the well is monitored and valve means (28) opening rate reduced on detection of a greater than predetermined increase in flow rate. A method of controlling the oil production is also provided wherein flow rate from the well is monitored and a flow regulating device (28) in the flow path from the well controlled in accordance with that monitored flow rate which is indicative of the onset of slugging.

This invention relates to a method for startup of production in an oilwell, and, more generally, to a method of control of oil production.

The production fluid recovered from an oil well normally comprises amixture of oil products, water and gas in varying proportions. Undersome circumstances, in order to facilitate flow to the surface, asuitable gas is injected into the well production casing, such astowards its lower end, whereby to be entrained in the production liquid.This has the effect of reducing the effective density of the fluidwhereby to improve flow to the surface. When starting up production in awell where this gas lift technique is used , some difficulty may arisein that the gas as admitted, may instead of being homogenously entrainedin the production fluid, "break out" and form large discrete regions ofgas within the well casing. The phenomenon known as "slugging", wherebyirregular flow of production fluid from the well occurs, will thenarise. This irregular flow is due to alternating flows of gas andproduction of fluid from the well. Generally, this phenomenon arisesbecause too much gas is injected relative to the quantity of productionfluid flowing up the well production casing. Slugging is an undesirablephenomenon since it results in waste of gas, which may be in relativelyshort supply Slugging also disrupts the orderly processing of theproduction fluid and may lead to damage to the oil reservoir.Furthermore, if the balance of gas is too great the entire flow of fluidmay be cut off.

In one aspect, the invention has for its object to provide a method tostartup of oil production in an oil well which lessens the possibilityof occurrence of slugging.

In one aspect, the invention provides a method of startup of oilproduction in an oil well, wherein gas is injected into the well fluidto be recovered whereby to facilitate lifting of the fluid,characterised in that while controlling the inlet flow of the said gas,valve means controlling fluid flow from the well is progressivelyopened. Preferably, the flow rate of fluid from the well is monitoredand the rate of opening of the valve means is varied whereby to reducethe rate of opening on detection of an increase in flow rate which isgreater than a predetermined rate. The inlet flow of the gas may bemaintained substantially constant.

The invention also provides a method of controlling oil production in anoil well using gas injection to facilitate lifting, wherein the flowrate of fluid from the well is monitored and a flow regulating device inthe flow path from the well is controlled in accordance with themonitored flow rate to reduce the flow rate when the flow rate, asmonitored, is indicative of onset of slugging, such as when an increasein flow rate is detected.

The invention is further described by way of example only with referenceto the accompanying drawings in which:

FIG. 1 is a diagram of an oil well adapted for practising the presentinvention;

FIG. 2 is a diagram illustrating the manner in which a well outletcontrol choke in the well of FIG. 1 is controlled; and

FIG. 3 is a diagram illustrating the manner of control of the welloutlet control choke.

In FIG. 1, an oil well production casing 10 is shown as having an outercasing 12 and an inner casing 14. The inner casing 14 extends into theoil reservoir 16 from which oil containing fluid is to be recovered, forflow of the fluid up the casing 14 and thence away from the well via asuitable outlet duct 20. The outer casing 12 is connected via a duct 22to a source 24 of pressurized gas. The inner casing 14 has apertures atsuitable positions such as adjacent the base thereof for admission ofgas in to the casing 14. The so admitted gas is entrained in the fluidflowing up casing 14 whereby, in accordance with conventional practice,to lessen the effective density of the fluid and to facilitate liftingof the fluid to the surface for outflow along duct 20.

Duct 20 is shown as having a valve or "choke" 28 positioned therein,this being operable to close off flow from the duct 20 or to present acontrollable sized opening for flow therethrough. A vortex meter 30 isalso positioned in duct 20 for measuring fluid flow rate in the duct 20,meter 30 being connected to an electronic or other controller 34 forcontrolling the valve 28. Thus the choke 28 may be electrically orpneumatically operated, the extent of opening of the choke beingcontrollable in accordance with fluid pressure or electrical signal fromthe control device 34.

Also shown, in duct 22 is a vortex meter 40 for measuring gas flow inthe duct 22, a valve 42 operable to control gas flow through the duct22, and a controller 46, such as an electrical or pneumatic device,effective to control valve 42 in the same manner as choke 28 iscontrolled by controller 34.

It has been found that good results are obtained, in terms of reducingslugging, if during startup of production the flow of the gas throughduct 22 is made, initially, equal to substantially the optimumanticipated flow and, preferably, maintained substantially at that rate.Starting with choke 28 closed, the choke 28 is then gradually andsmoothly opened such as illustrated in the graph 2 where the plot 48shown illustrates the manner of variation of the choke opening withtime. The full choke opening may be reached over a time period "x"indicated which may be of order of 5 to 30 minutes. Thus opening of thechoke may be controlled by the controller 34 by application of a rampsignal to the choke 28.

In operation, too, the flow meter 30 measures the flow rate through theduct 20 and the rate of opening of the choke 28 (i.e. the slope of theramp signal applied thereto) is varied under control of the controller34. More particularly, when the flow rate is found to increase at morethan a predetermined rate, represented in FIG. 3 by phantom line 50 atthe region 52 shown, the controller 34 is effective to reduce the rateof opening of the choke 28 whereby to tend to restore the flow rateincrease to conform to the desired rate represented by line 50.

While the invention has been described with reference: to the use ofvortex meters for measuring flow, other kinds of meters may be employed.However, as mentioned in Australian patent specification 30828/84,vortex meters are quite suitable for measuring mixed phase flows such asoccur in the duct 30.

In a modification (not illustrated) the flow rate of the gas through theduct 22 may be varied during start-up. In particular, it may beincreased in some predetermined fashion. The control of the gas flow iseffected as desired by the controller 46. While the invention has beendescribed in the context of a production start-up technique, it is alsoapplicable to control of oil production generally. Thus, the controller34 may act during ordinary operation of the well to decrease the flowopening therethrough under the condition of detection of increased flowby flow meter 30, or otherwise in response to detection of a conditionpossibly corresponding to onset of slugging.

The described arrangement has been advanced merely by way of explanationand many modifications may be made thereto without departing from thespirit and scope of the invention as defined in the appended claims.

We claim:
 1. A method of startup of oil production in a continuousgas-lift oil well comprising the steps of:injecting gas into the wellfluid to be recovered to reduce its effective density so as tofacilitate lifting of the fluid; monitoring the flow rate of the fluidfrom the well; progressively opening valve means controlling the fluidflow from the well; and controlling said opening of the valve means suchthat the rate of opening thereof is varied to reduce the rate of openingon detection of an increase in monitored flow rate which is greater thana predetermined rate, whereby to reduce the tendency for slugging.
 2. Amethod for startup of oil production in a continuous gas-lift oil wellas claimed in claim 1, wherein the inlet flow of the gas is maintainedsubstantially constant.
 3. A method for startup of oil production in acontinuous gas-lift oil well as claimed in claim 1, wherein the fluidflow rate from the well is monitored by a vortex meter.
 4. A method ofoil production in a continuous gas-lift oil well comprising the stepsof:injecting gas into the well fluid to be recovered to reduce itseffective density so as to facilitate lifting of the fluid; monitoringthe flow rate of the fluid from the well; and controlling a flowregulating device in the flow path of the fluid from the well inaccordance with the monitored flow rate to reduce the flow rate when theflow rate, as monitored, is indicative of the onset of slugging.
 5. Amethod of oil production in a continuous gas-lift oil well as claimed inclaim 4, wherein said reduction in said flow rate is effected when anincrease in said flow rate is detected.
 6. A method of oil production ina continuous gas-lift oil well as claimed in claim 4, wherein the fluidrate from the well is monitored by a vortex meter.